British light heavyweight Joshua Buatsi secured a victory yet disappointing start to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a majority decision in a competitive ten-round bout at the Manchester venue.
But the challenger landed significant shots, delivering effective single shots in a fight where the approaches didn't complement each other, with constant grabbing marring the contest.
The scoring judges judged it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my best showing but what do champions do? They prevail," the victor stated in the ring as he was met by disapproval from the audience.
The Londoner bounced back after his first professional defeat - an memorable fight with his previous opponent in last winter - to secure a twentieth professional win.
Several boxing experts thought Parker, thirty-one, deserved the win but the contender suffered the second setback of his 28-match professional journey.
The Champion Earns Win in Dull Match
His career development has slowed in recent times through contract problems and long spells of inactivity.
Earlier forecast as the next star of the British fight scene, he now stands trying to realize his potential - perhaps in what feels like a final roll of the dice - under new promotional backing.
He started carefully, with both competitors ready to be aggressive in a calculated opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in two years ago after suffering a hand injury during the bout, was making just his second bout at light-heavyweight.
By the fight's midpoint, the underdog had kept it close, making life awkward for the favorite, who worked behind a protective stance to barely take the cleaner periods.
The audience's tolerance diminished amid constant clinching, with the challenger going down various instances during close exchanges.
The underdog closed well, but several stanzas were challenging to assess. Nevertheless, ex-champion Carl Frampton - commentating on Dazn - had it significantly in favor for the challenger, giving Buatsi just one round.
The victor advances, but with the likes of power puncher David Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - on this evidence - still looks steep.
Ricky Hatton Memorial Fuels All-Manchester Fight
In the supporting bout, Arthur defeated Rea by divided decision in a excellent Manchester vs Manchester contest to win the European light-heavyweight belt.
The venue became quiet for a extremely emotional memorial prior to the bout as a bell ceremony tolled in memory of the city's native Ricky Hatton, who succumbed at age 46 in last month.
It was the first major televised match card in the location since Hatton's passing. As the final chime ended, the quiet became a roar of "there's only one Ricky Hatton".
The competition inside the ropes matched the feeling. The eventual winner was knocked down by a left hook directly to the jaw in the early round, rising shakily to his footing on the eight count.
But the red-colored equipment of the fighter soon pressed ahead again. Across the ring, Rea - in competitive blue - was damaged soon, noticeable damage forming under his eye as the duo exchanged punishing blows.
The challenger, 27, landed power punches but Arthur, thirty-four, responded in kind with effective uppercuts as the pace rarely dropped over the full distance.
Arthur edged the verdict with official scores of draw, close margin and clearer margin, but the two athletes were determined and brave, all the qualities their hero Hatton stood for.
